U.S. Pat. No. 4,921,767, issued to Datta et al., on May 1, 1990, describes the basic method of manufacturing a luminescent screen for a color CRT by the electrophotographic screening (EPS) process, using dry-powdered, triboelectrically-charged screen structure materials that are serially deposited onto a suitable photoreceptor disposed on an interior surface of a faceplate panel. The photoreceptor comprises, preferably, an organic conductive (OC) layer having a thickness of about 1 micron (.mu.m) and an overlying organic photoconductive (OPC) layer having a thickness of about 5-6 .mu.m. In the above-referenced patent, the OPC layer is a volatilizable organic polymeric material, such as polyvinyl carbazole, n-ethyl carbazole, n-vinyl carbazole or tetra phenyl butatriene (TPBT), dissolved in a suitable binder, such as polymethyl methacrylate or polypropylene carbonate. In the EPS process, the OPC layer must be suitably dried and the underlying faceplate panel must be cooled to a temperature of about 35.degree. C., or less, in order for the OPC layer to accept and retain an electrostatic charge from a charging device. It is known to dry the OPC layer with a metal rod sheath-heater, but about 30-45 seconds are required to dry the OPC layer by this method. Additionally, this relatively long drying time warms the faceplate glass substantially, and additional time is required to cool the glass and the OPC layer to below 35.degree. C. The relatively long heating and cooling times are not a problem in a laboratory environment; however, such long processing times are incompatible with efficient commercial production, where each step in the process should, ideally, take no more than about 10, and, preferably about 8, seconds for panels with a diagonal dimension of 51 centimeters (cm), or less. The OC layer presents no such problem, because it has an optimum thickness of only about 1 .mu.m and can be air-dried rapidly.
The formulation of the OPC layer recently has been changed from that of the above-referenced patent, to reduce its spectral sensitivity beyond 550 nanometers (nm), so that the screen may be processed in yellow light, rather than in the dark, as required for the prior OPC material. The present OPC layer comprises a solution of polystyrene resin; 2,4-DMPBT as an electron donor material; TNF and 2-EAQ as electron acceptor materials; a surfactant; and a suitable solvent. The improved OPC layer may be applied by spin-coating or spraying the above-described solution onto the interior surface of the faceplate panel. The dried OPC layer, made with the present solution, also has an optimum thickness of about 5-6 .mu.m. However, if the metal rod sheath heaters are used to dry the improved OPC layer, the drying time remains about 30-45 seconds, resulting in the unintended heating of the faceplate panel, thereby requiting additional time to cool the panel to a temperature of less than about 35.degree. C., to facilitate subsequent processing.
In order to provide an OPC layer that readily accepts and retains an electrostatic charge, and is compatible with commercial production cycle times of about 8 seconds, a more efficient method of conditioning the OPC layer 34, without heating the panel 12, is required.